1. Field of the Invention
The present invention relates to a cable-type steering device in which a steering wheel and a gear box are connected to each other by a flexible cable such as a Bowden cable.
2. Description of Related Art
A conventional steering device for a vehicle is designed in such a manner that a steering shaft having a steering wheel at its upper end is connected at its lower end to a gear box, so that a steering torque inputted to the steering wheel is transmitted through the steering shaft to a rack and pinion mechanism mounted within the gear box.
However, if the steering wheel and the gear box are connected to each other using the steering shaft, it is difficult to freely select the position of the steering wheel relative to the position of the gear box. For this reason, there is encountered a problem that the degree of freedom in the design is substantially limited, and the gear box cannot be commonly used in a right-hand steered vehicle and a left-hand steered vehicle. Moreover, another problem is that the vibration inputted to a tire from a road surface and the vibration of an engine are inputted to the steering wheel through the steering shaft and hence, the silence within a vehicle compartment and the riding comfort are impeded by such vibrations.
Therefore, there is a proposed cable-type steering device which employs a flexible transmitting means such as a Bowden wire and line in place of the conventional steering shaft (see Japanese Patent Application Laid-open No.8-2431).
If the construction of the proposed cable-type steering device is used, the position of the steering wheel relative to the position of the gear box can be freely selected. Moreover, it will be difficult to transmit the vibration of the gear box to the steering wheel. Hence, the above-described problems can be solved.
A conventionally well-known electric power-steering device is designed so that a steering torque of a steering wheel is detected, and an output corresponding to the steering torque is generated by a motor for a power-steering operation to assist in the operation of the steering wheel performed by a driver. A torsion bar is incorporated in a path of transmission of the steering torque, and the detection of the steering torque is achieved by detecting an amount of torsion bar distorted due to the steering torque by a differential transformer.
However, because the conventional steering torque detecting means detects the steering torque based on the amount of torsion bar distorted, there is a problem in that the structure is complicated and the cost is increased. Also, the distortion of the torsion bar causes the steering rigidity to be decreased, thereby providing an adverse influence to the steering feeling.